Influence of cyclin type and dose on mitotic entry and progression in the early Drosophila embryo

Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143, USA.
The Journal of Cell Biology (Impact Factor: 9.83). 04/2009; 184(5):639-46. DOI: 10.1083/jcb.200810012
Source: PubMed


Cyclins are key cell cycle regulators, yet few analyses test their role in timing the events that they regulate. We used RNA interference and real-time visualization in embryos to define the events regulated by each of the three mitotic cyclins of Drosophila melanogaster, CycA, CycB, and CycB3. Each individual and pairwise knockdown results in distinct mitotic phenotypes. For example, mitosis without metaphase occurs upon knockdown of CycA and CycB. To separate the role of cyclin levels from the influences of cyclin type, we knocked down two cyclins and reduced the gene dose of the one remaining cyclin. This reduction did not prolong interphase but instead interrupted mitotic progression. Mitotic prophase chromosomes formed, centrosomes divided, and nuclei exited mitosis without executing later events. This prompt but curtailed mitosis shows that accumulation of cyclin function does not directly time mitotic entry in these early embryonic cycles and that cyclin function can be sufficient for some mitotic events although inadequate for others.

Download full-text


Available from: Patrick H O'Farrell
  • Source
    • "While they do not look at cyclinB, this gene is also a target of mRNA decay at the maternal-to-zygotic transition and may be also targeted by the PIWI/piRNA pathway (Benoit et al., 2009). Considering the variety of targets aberrantly stabilized by loss of some piRNA pathway components, it is not a stretch to consider inappropriate regulation of cyclin B mRNAs, levels of which are essential to the normal progression of mitosis during Drosophila embryogenesis (McCleland et al., 2009). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Small RNAs impact several cellular processes through gene regulation. Argonaute proteins bind small RNAs to form effector complexes that control transcriptional and post-transcriptional gene expression. PIWI proteins belong to the Argonaute protein family, and bind PIWI-interacting RNAs (piRNAs). They are highly abundant in the germline, but are also expressed in some somatic tissues. The PIWI/piRNA pathway has a role in transposon repression in Drosophila, which occurs both by epigenetic regulation and post-transcriptional degradation of transposon mRNAs. These functions are conserved, but clear differences in the extent and mechanism of transposon repression exist between species. Mutations in piwi genes lead to the upregulation of transposon mRNAs. It is hypothesized that this increased transposon mobilization leads to genomic instability and thus sterility, although no causal link has been established between transposon upregulation and genome instability. An alternative scenario could be that piwi mutations directly affect genomic instability, and thus lead to increased transposon expression. We propose that the PIWI/piRNA pathway controls genome stability in several ways: suppression of transposons, direct regulation of chromatin architecture, and regulation of genes that control important biological processes related to genome stability. The PIWI/piRNA pathway also regulates at least some, if not many, protein-coding genes, which further lends support to the idea that piwi genes may have broader functions beyond transposon repression. An intriguing possibility is that the PIWI/piRNA pathway is using transposon sequences to coordinate the expression of large groups of genes to regulate cellular function. Mol. Reprod. Dev. © 2013 Wiley Periodicals, Inc.
    Full-text · Article · Aug 2013 · Molecular Reproduction and Development
  • Source
    • "As astutely pointed out more than 50 years ago by Daniel Mazia, " We know practically nothing about what happens during the usual pause at metaphase except that something is happening! " (Mazia 1961). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Chromosome positioning at the equator of the mitotic spindle emerges out of a relatively entropic background. At this moment, termed metaphase, all kinetochores have typically captured microtubules leading to satisfaction of the spindle-assembly checkpoint, but the cell does not enter anaphase immediately. The waiting time in metaphase is related to the kinetics of securin and cyclin B1 degradation, which trigger sister-chromatid separation and promote anaphase processivity, respectively. Yet, as judged by metaphase duration, such kinetics vary widely between cell types and organisms, with no evident correlation to ploidy or cell size. During metaphase, many animal and plant spindles are also characterized by a conspicuous "flux" activity characterized by continuous poleward translocation of spindle microtubules, which maintain steady-state length and position. Whether spindle microtubule flux plays a specific role during metaphase remains arguable. Based on known experimental parameters, we have performed a comparative analysis amongst different cell types from different organisms and show that spindle length, metaphase duration and flux velocity combine within each system to obey a quasi-universal rule. As so, knowledge of two of these parameters is enough to estimate the third. This trend indicates that metaphase duration is tuned to allow approximately one kinetochore-to-pole round of microtubule flux. We propose that the time cells spend in metaphase evolved as a quality enhancement step that allows for the uniform stabilization/correction of kinetochore-microtubule attachments, thereby promoting mitotic fidelity.
    Preview · Article · Jul 2012 · Chromosome Research
  • Source
    • "Likewise, ablation of the Cdk2 activating partners cyclin E1 and E2 in mouse embryonic fibroblasts was not associated with any centrosomal defects [83]. In support of studies done in mammalian cells, various combinatorial knockdowns of two mitotic cyclins (CycA, CycB, and CycB3), and reduction of the dosage of the remaining cyclins in Drosophila embryonic syncytial divisions allows centrosomes to duplicate, while cells do not enter mitosis [84]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Because centrosome amplification generates aneuploidy and since centrosome amplification is ubiquitous in human tumors, a strong case is made for centrosome amplification being a major force in tumor biogenesis. Various evidence showing that oncogenes and altered tumor suppressors lead to centrosome amplification and aneuploidy suggests that oncogenes and altered tumor suppressors are a major source of genomic instability in tumors, and that they generate those abnormal processes to initiate and sustain tumorigenesis. We discuss how altered tumor suppressors and oncogenes utilize the cell cycle regulatory machinery to signal centrosome amplification and aneuploidy.
    Full-text · Article · Jan 2011 · Cell Division
Show more